Princeton Election Consortium

A first draft of electoral history. Since 2004

Amicus Brief in Gill v. Whitford

August 30th, 2017, 10:39pm by Sam Wang

Today we submitted our amicus brief (read the PDF) in the case of Gill v. Whitford. The authors are Heather Gerken, Jonathan N. Katz, Gary King, Larry Sabato, and me. In it, we argue that the Supreme Court should define basic fairness in redistricting using the concept of partisan symmetry. We use this idea to suggest simple statistical tests that could be used as a manageable standard to identify extreme partisan gerrymandering.

For example, are Democratic districts more packed than Republican districts than would be expected from inadvertent effects? That can be determined using Student’s t-test, the most common test in the sciences, invented by an experimental brewer at the Guinness Beer Company over 100 years ago.

If the Court accepts our recommendation, then there would be, for the first time, a way for courts to say when a partisan gerrymander has gone too far. This has been an unresolved issue since the mid-1980′s, when the Court first said that partisan gerrymandering was a violation of the U.S. Constitution. Now that partisan gerrymanders have become rampant in the last redistricting cycle, we believe it is time for the Supreme Court to act.

If you want to learn more about symmetry standards, I invite you to visit the Princeton Gerrymandering Project. You can also support our work here.

→ Post a commentTags: Redistricting · U.S. Institutions

Gerrymandering vs. Math: Who will win?

August 29th, 2017, 2:23pm by Sam Wang

From Emily Bazelon, a sharp look at partisan gerrymandering. Her thinking and analysis will resonate with fans of the Princeton Gerrymandering Project.

We’ll have more coverage soon, once the Supreme Court amicus filing deadline has passed…

→ Post a commentTags: Redistricting

Democratic Partisan Gerrymanders, 1972-present

August 23rd, 2017, 12:39am by Sam Wang

The Princeton Gerrymandering Project makes it easy to browse all gerrymandering offenses for a given year. We are now starting to cross-reference these offenses with who had control over the redistricting process. It’s a daunting task, but our statistical analyst Brian Remlinger is on the case.

Brian has found something interesting: from 1972 until now, Democratic extreme partisan gerrymanders are surprisingly rare. What’s going on? [Read more →]

→ 4 CommentsTags: House · Redistricting

Politics & Polls: Charlottesville and our broken public discourse

August 17th, 2017, 12:09pm by Sam Wang

The route between public outrage and consequences for President Trump seems quite broken. Why? Julian Zelizer and I chew it over in the new Politics & Polls. The opening is especially lively. Later we get into the regular nerdery.

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The Princeton Gerrymandering Project is live!

August 4th, 2017, 7:34am by Sam Wang

I am happy to announce our revamped site at This is part of the Princeton Gerrymandering Project’s tooling up for the coming several years of work by courts and reformers.

The site now has an interactive map showing the results of three simple gerrymandering tests, applied in all the states. It allows you to upload data more conveniently than before. Finally, it has a tutorial, as well as links to background reading and current court cases. Check it out!

All of this was done by the team: Rob Whitaker, Brian Remlinger, Aimee Otsu, Sung Chang, and Naomi Lake. Hats off to their great effort.

→ 10 CommentsTags: Redistricting · Site News

Partisan gerrymandering case to be argued before Supreme Court on October 3rd

July 19th, 2017, 2:22pm by Sam Wang

Just in: oral arguments in Gill v. Whitford will take place at 10:00am on Tuesday, October 3rd. It’s the second day of the fall term.

→ 3 CommentsTags: Redistricting

Partisan Gerrymandering Across the 50 States

July 16th, 2017, 8:49am by Sam Wang

Note: I’ll pretty this up later. In the meantime, the files are available for you to download and inspect at the end of this post.

Over at the Associated Press, reporter David Lieb has published a new, in-depth analysis of the effects of gerrymandering in the 2016 Congressional and statehouse elections. The analysis found that the same states identified as partisan gerrymanders in 2012 and 2014 in my Stanford Law Review article — North Carolina, Michigan, Pennsylvania, and Maryland — also show clear signs of advantage to the same political paty.

The analysis is important for two reasons: (1) It means that the advantages built into the district maps in 2012 aren’t dissipating, and that these gerrymanders will likely hold up through the 2020 elections, and (2) These advantages aren’t an accident, because they are echoed at the level of state legislatures. In short, the parties that were in power in 2011 are likely to have a strong hand in drawing the maps again in 2021. They will go unfettered unless the opposing party gains the governorship*.

While the AP report primarily relies on the “efficiency gap” analysis, the Princeton Gerrymandering Project provided a separate t-test** analysis of election results for the article. The agreement between the two tests is striking. Virtually*** every state flagged by the t-test at the Congressional level is also flagged by the efficiency gap. Generally, we have found that the efficiency gap does well except for having a higher false-positive rate than the t-test, which is unsurprising since the t-test has such a venerable history. At the state legislative level, 4 of the 6 worst offenders according to the efficiency gap are also captured by the t-test with exceedingly low p-values.

The results of our analysis of Congressional races can be found here, and results for state house elections can be found here.

I thank Brian Remlinger and Naomi Lake for assistance with this post.


*Currently, the opposition party holds the governor’s mansion in Pennsylvania (Tom Wolf, a Democrat) and Maryland (Larry Hogan, a Republican). Note that in North Carolina, the governor has no role in redistricting.

**A note on statistical testing: Our analysis used one- or two-tailed t-tests, depending on redistricting authority. For states with single party control of redistricting, we carried out one-tailed tests for advantage in the direction of that party. For states with bipartisan or nonpartisan redistricting, we carried out two-tailed tests.

***The exception is California, whose top-two primary system complicates analysis.

→ 2 CommentsTags: 2012 Election · 2014 Election · 2016 Election · governors · Redistricting

Benjamin Wittes on Politics & Polls

July 13th, 2017, 4:52pm by Sam Wang

Benjamin Wittes of Lawfare joined Julian Zelizer and me today on Politics & Polls. He gave us an unsparing look at potential crimes & what the Trump-Russia scandal looks like to the national-security community. Listen:

→ 1 CommentTags: President · Princeton · U.S. Institutions

Sharp cutbacks at HuffPost Pollster

June 15th, 2017, 2:21pm by Sam Wang

This is terrible news. As part of cutbacks at the Huffington Post, the tracking of polls will be curtailed dramatically. As reported by HuffPollster’s Ariel Edwards-Levy, they will only be tracking Trump’s favorability/unfavorability. All the other charts are now frozen. Evidently that includes the
generic House ballot, which I think is quite important.

This is a tremendous loss. The Princeton Election Consortium relies on their feed. They curate data, they apply their judgment, and they generate a structured API for dozens of races every year. It’s been a wonderful resource.

Personally, I would be willing to pay for such a feed. However, I’ve never been asked. Also, it’s not obvious whether there are enough subscribers to sustain their work.

I hope they re-expand operations in the future. In the meantime, I thank the many people who make HuffPost Pollster possible: Ariel Edwards-Levy, Janie Velencia, and before that Natalie Jackson, and before that Mark Blumenthal, and too many others to list here.

Here’s one of my favorite charts of theirs: the generic Congressional ballot. It’s for aficionados…but I do love it.

→ 7 CommentsTags: Politics

R.I.P., Adam West

June 10th, 2017, 11:54am by Sam Wang

My favorite version of Batman.

→ 1 CommentTags: Uncategorized